Yarn

ABSTRACT

A yarn having characteristics required in a gland packing is obtained by, when the yarn is to be constructed by fibers such as organic fibers, finding relationships between the required characteristics and the value of the limiting oxygen index (LOI), and adequately defining the level of the required characteristics. A yarn is formed by twisting fibers having a limiting oxygen index of 21 to 30, preferably 22 to 26. The fibers contain fibers in which a flat ratio is defined as 1.1 to 2, the flat ratio being a value obtained by dividing the maximum value of an interval between two parallel straight lines in a state where a section of each of the fibers is interposed between the straight lines, by the minimum value. The fibers contain fibers in each of which a sectional shape has one or more recesses having a depth of 0.4 μm or more.

TECHNICAL FIELD

The present invention relates to a yarn which is suitably used in agland packing that is used as a sealing component for a fluid apparatussuch as a pump or a valve.

BACKGROUND ART

As a conventional art relating to a gland packing which is to be used ina shaft seal part of a fluid apparatus such as a pump or a valve, and ayarn used in the packing, well known is a technique in which expandedgraphite is used as disclosed in Patent Literature 1. Expanded graphitehas advantages that it is excellent in flexibility and chemicalresistance, high in adhesiveness, and durable at high temperature, butalso has drawbacks that it has a very low tensile strength, and isbrittle and easy to break.

Therefore, a yarn formed by fibers which are high in strength and wearresistance, and a gland packing in which such a yarn is twisted orbraided into a cord-like shape are produced. For example, fiber productsare known which are disclosed in Patent Literatures 2 and 3, and inwhich acrylic fiber are used. In addition to acrylic fibers andmodacrylic fibers, other various fibers such as rayon, cellulose, hemp,cotton, and polyvinyl alcohol may be used as organic fibers which areuseful in such fiber products.

Organic fibers have various features depending on the material, such ashigh strength and wear resistance, low thermal resistance andhygroscopicity, excellent resistance to high temperature and chemicalresistance, low resistance to ultra violet light, and high power ofresistance. Therefore, it is requested to select fibers made of amaterial suitable for the purpose.

Namely, fibers (organic fibers) forming a yarn are requested to reduceto some extent friction (friction coefficient) which is critical insliding between a gland packing and a shaft of a fluid apparatus such asa pump, or to have flexibility which is important in compatibility witha gland portion or a shaft.

As a factor indicating the characteristics of fibers which are requestedto have various characteristics, there is the limiting oxygen index(LOI), as disclosed in Patent Literature 4. The limiting oxygen index isone of methods of evaluating the ease of burning of a material such asplastics or fibers. While changing the ratio of “nitrogenmolecules/oxygen molecules” of the air, the oxygen concentration of thelimit of causing ignition, i.e., the limiting oxygen index (LOI) isobtained.

PRIOR ART LITERATURE Patent Literature

-   [Patent Literature 1]: Japanese Patent Application Laid-Open No.    59-068387-   [Patent Literature 2]: Japanese Patent Application Laid-Open No.    11-217723-   [Patent Literature 3]: Japanese Patent Application Laid-Open No.    09-078375-   [Patent Literature 4]: Japanese Patent Application Laid-Open No.    2013-067920

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

Therefore, it is an object of the invention to enable a yarn havingcharacteristics which are required in a gland packing, to be obtainedby, when the yarn is constructed by fibers such as organic fibers,finding relationships between the required characteristics and the valueof the limiting oxygen index, and adequately defining the level of therequired characteristics.

Means for Solving the Problems

The first invention is characterized in that, in a yarn,

fibers s having a limiting oxygen index of 21 to 30 are twisted.

The second invention is characterized in that, in the yarn of the firstinvention,

the limiting oxygen index is 22 to 26.

The third invention is characterized in that, in the yarn of the firstor second invention,

the fibers s contain fibers in which a flat ratio f is defined as 1.1 to2, the flat ratio being a value which is obtained by dividing a maximumvalue a of an interval between two parallel straight lines L1, L2 in astate where a section of each of the fibers is interposed between thestraight lines L1, L2, by a minimum value b.

The fourth invention is characterized in that, in the third invention,

the flat ratio f is defined as 1.4 to 1.6.

The fifth invention is characterized in that, in the yarn of any one ofthe first to fourth inventions,

the fibers s contain fibers in each of which a sectional shape has oneor more recesses 1.

The sixth invention is characterized in that, in the yarn of the fifthinvention,

a depth h of the recess 1 is 0.4 μm or more.

The seventh invention is characterized in that, in the yarn of any oneof the first to sixth inventions,

the fibers s contain modacrylic fibers.

The eighth invention is characterized in that, in the yarn of theseventh invention,

the modacrylic fibers are acrylonitrile-vinyl acetate copolymer fibers.

Effects of the Invention

According to the first invention, since the limiting oxygen index of thefibers is 21 or more, the friction coefficient can be reduced. In thecase where a gland packing is formed by using the yarn, therefore, it ispossible to obtain an advantage that friction with a slide member suchas a shaft is small.

Since the limiting oxygen index of the fibers is 30 or less,furthermore, the yarn is highly flexible. In the case where a glandpacking is formed by using the yarn, therefore, the conformability withthe slide member such as a shaft is improved, and there is an advantagethat it is possible to attain an excellent sealing property in whichless leakage occurs.

As a result, in the case where a yarn is constructed by fibers such asorganic fibers, when relationships between the required characteristicsand the value of the limiting oxygen index are found, and the level ofthe required characteristics is adequately defined, it is possible toprovide a yarn having characteristics which are required in a glandpacking.

In this case, when the limiting oxygen index is 22 to 26 as in thesecond invention, it is possible to provide a yarn in which the effectdue to the configuration of the first invention can be further enhanced.

According to the third invention, a yarn which is obtained by twistingfibers of a flat ratio f of f≧1.1, and a gland packing which uses theyarn can easily hold an impregnating material, and a yarn which isobtained by twisting fibers of f≦2, and a gland packing which uses theyarn can sufficiently reduce stress relaxation, and ensure and maintainstress required for sealing.

When fibers in which 1.1≦f≦2 exist, therefore, it is possible to attainthe above-described effects, i.e., v “impregnating material can beeasily held” and z “stress required for sealing can be ensured andmaintained”. A configuration where fibers in which 1.1≦f≦2 exist in 50%or more is preferable because the effects v and z can be clearlyattained.

In this case, when the flat ratio is 1.4≦f≦1.6 as in the fourthinvention, the effects v and z can be enhanced.

According to the fifth invention, since fibers having one or morerecesses exist, an impregnating material can be held by the recesses.The yarn is formed by using fibers containing the fibers each having oneor more recesses, and therefore it is possible to provide a yarn whichcan substantially provide the advantage that an impregnating materialcan be held. A configuration where fibers each having one or morerecesses exist in 50% or more is preferable because the above-describedeffect, i.e., w “impregnating material can be held” can be clearlyattained.

In this case, a configuration where the depth of the recess is 0.4 μm ormore as in the sixth invention is preferable from the viewpoint that theimpregnating material can be easily held. A configuration where thedepth is 0.6 μm or more is further preferable.

As fibers to be used, fibers which have modacrylic fibers as in theseventh invention are preferable. A configuration where the modacrylicfibers are acrylonitrile-vinyl acetate copolymer fibers as in the eighthinvention is advantageous.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing sectional shapes of single fibers.

FIG. 2 is a view showing a sectional shape and flat ratio of a fiber.

FIG. 3 is a diagram showing the configuration of a leakage testingapparatus.

FIG. 4 is a detail view of a leakage testing unit in FIG. 3.

FIG. 5 is a diagram showing a stress relaxation testing apparatus.

FIG. 6 is a diagram showing a friction testing apparatus.

FIG. 7 is a table showing results of a leakage test and a friction test.

FIG. 8 is a graph illustrating the test results shown in FIG. 7.

FIG. 9 is a table showing relationships among the flat ratio, theimpregnation ratio, and stress relaxation.

FIG. 10 is a graph illustrating the relationships shown in FIG. 9.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments of the yarn of the invention will be describedwith reference to the drawings. In the following description, thelimiting oxygen index is abbreviated as “LOI”.

Embodiment 1

A yarn of Embodiment 1 is characterized in that the yarn is formed bytwisting fibers having an LOI of 21 to 30. Namely, the value e of theLOI of the fibers is 21≦e≦30.

Examples of fibers having an LOI value e of 21≦e≦30 are acrylic fibers,modacrylic fibers, rayon, cellulose, hemp, cotton, and polyvinylalcohol.

Acrylic fibers include those formed by a polymer containing 50 wt. % ormore of acrylonitrile. The polymer may be a copolymer of acrylonitrileand an unsaturated monomer which is copolymerizable with acrylonitrile,as far as the polymer contains 50 wt. % or more of acrylonitrile.

Examples of the unsaturated monomer which is copolymerizable withacrylonitrile are: an acrylic ester such as methyl acrylate, ethylacrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate,2-hydroxyethyl acrylate, and hydroxypropyl acrylate; a methacrylic estersuch as ethyl methacrylate, isopropyl methacrylate, n-butylmethacrylate, isobutyl methacrylate, t-butyl methacrylate, n-hexylmethacrylate, cyclohexyl methacrylate, lauryl methacrylate,2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, anddiethylaminoethyl methacrylate; and an unsaturated monomer such asacrylic acid, methacrylic acid, maleic acid, itaconic acid, acrylamide,N-methylolacrylamide, diacetoneacrylamide, styrene, vinyl toluene, vinylacetate, vinyl chloride, vinylidene chloride, vinyl bromide, vinylidenebromide, vinyl fluoride, and vinylidene fluoride.

Moreover, a monomer which is to be copolymerized is p-sulfophenylmethallylether, methallylsulfonate, allylsulfonate, styrenesulfonate,2-acrylamide-2-methylpropanesulfonic acid, their alkali metal salts, andor like.

In adjustment of the LOI value e of the fibers, means for exposing thefibers in an air atmosphere at a temperature of 200 to 400° C. for 1 to10 hours may be used.

Next, the flat ratio of a fiber will be described.

The fibers (single fibers) s forming the yarn of Embodiment 1 containthose in which the flat ratio f is defined as 1.1 to 2, the flat ratiobeing a value which is obtained by dividing the maximum value a of theinterval between two parallel straight lines L1, L2 in a state where asection of each of the fibers is interposed between the straight linesL1, L2 as shown in FIGS. 1 and 2, by the minimum value b.

In the case of a fiber s having a kidney-shaped sectional shape shown inFIG. 2, namely, the maximum value among intervals between two parallelstraight lines L1, L2 is a, and the minimum value is b. In this case,the flat ratio is f=(a/b).

When fibers having a flat ratio f of 1.1≦f≦2 exist, it is possible toattain the above-described effects v and z, and, when fibers in which1.1≦f≦2 exist in 50% or more, it is preferable because the effects v andz can be clearly attained.

In the case where the number of fibers forming a yarn Y is 100, forexample, the fibers contain 50 or more fibers in which the flat ratio fis 1.1≦f≦2. It is more preferable that the flat ratio f is defined as1.4 to 1.6.

The fibers (single fibers) s forming the yarn contain those in which asectional shape has one or more recesses 1 (having a kidney-like shape)as shown in FIG. 2. When fibers having one or more recesses 1 exist, itis possible to substantially attain the effect w. A configuration wherefibers having one or more recesses exist in 50% or more is preferablebecause the effect w can be clearly attained.

A configuration where two or more recesses 1 exist, such as that wherethe sections of the fibers s have a gourd-like shape may be possible.Preferably, the depth h of the recess 1 shown in FIG. 2 is h≧0.4 μm fromthe viewpoint that an impregnating material is effectively held by therecesses 1. A configuration being h 0.6 μm is more preferable.

Although not illustrated, in fibers having a sectional shape in which arecess is not formed, the flat ratio f is 1.0≦f≦1.7, and the sectionalshape is formed only by curved lines. In fibers having a sectional shapein which, for example, one or more kidney-shaped recesses are formed,the flat ratio f is 1.1≦f≦4. In many of such fibers, the flat ratio fwas 1.2≦f≦1.7.

The sections of the fibers (single fibers) s have a diameter of 17±3 μm,and a length of 128±20 μm. The fibers have a fineness of 2 deniers. In asingle yarn obtained by spinning fibers, the weight due to a first twistof 90 turns per meter is 0.14 g/m. In a yarn obtained by twisting threesingle fibers, the weight due to a final twist of 40 turns per meter is0.43 g/m. A braided packing (gland packing) is formed by square knittingusing eight yarns, circular knitting using sixteen yarns, latticeknitting using thirty-two yarns, or the like.

The impregnation process is performed as follows. A braided glandpacking which is formed by using the yarn of the invention is immersedin an aqueous dispersion of a fluorine resin, and drawn up after apredetermined number of hours, and dried. The impregnation rate τ can beexpressed by:

τ={(x−y)/x}×100(unit: %)

where x indicates the weight after the impregnation, and y indicates theweight before the impregnation. The impregnation rate in the embodimentwas τ=45% to 50%.

After the impregnation, a hydrocarbon lubricant may be similarlyimpregnated.

(Apparatus and Method of Leakage Test, and Results)

FIG. 3 shows a leakage testing apparatus A. The leakage testingapparatus A is configured by arranging a leakage testing unit 2, abearing 3, a rotary joint 4, a torque detecting unit 5, a bearing 6, atransmission belt 7, an electric motor 8, a leakage measuring unit 9,and the like in a test frame 22 as shown in the figure.

As shown in FIG. 4, the leakage testing unit 2 has a fluid inlet 10, aseal box 11 including a sealing device B, a fluid outlet 12, etc. Thereference numeral 13 denotes a pump connected in a supply flow path 16through which a fluid (water or the like) in a tank 14 is supplied tothe fluid inlet 10.

A first thermometer 15 which measures the fluid temperature on the inletside of the fluid which is to be sealed is disposed in the supply flowpath 16. A second thermometer 18 which measures the fluid temperature onthe outlet side of the fluid is disposed in a discharge flow path 17which extends from the fluid outlet 12 to the tank 14.

As shown in FIG. 3, the leakage measuring unit 9 has a reservoir vessel9A which can receive and reserve a fluid leaking from the sealing deviceB, and a weighing device 9B which weighs the weight of the leaking fluidtogether with that of the reservoir vessel. The broken lines which aredrawn vertically downward in FIGS. 3 and 4 indicate diagrammatically thefalling path of the leakage fluid.

The sealing device B has a usual configuration. Namely, a receivingmember 20, a plurality of gland packings g, and a packing gland 21 areinserted into a cylindrical space defined by a gland portion 11A of theseal box 11 and a rotation shaft 19. The packing gland 21 is fastened toa flange 11 a of the gland portion 11A by bolts which are not shown,whereby the plurality of gland packings g are pressed in the axialdirection P to seal the interface between the gland portion 11A and therotation shaft 19.

The reference numeral 23 denotes a third thermometer which measures thetemperature of the jacket on the inlet side of the fluid to be sealed,and 24 denotes a fourth thermometer which measures the temperature ofthe jacket on the outlet side of the fluid to be sealed. Also a fifththermometer 25 which measures the temperature (packing temperature) ofthe gland packings g is disposed.

The leakage test method using the leakage testing apparatus A isperformed in the following manner. One set of five gland packings g (1set of 5 rings) having an inner diameter of 100 mm, an outer diameter of129 mm, and a height of 14.5 mm is installed in the gland portion 11A ofthe leakage testing apparatus A simulating a pump. Fresh water (fluid tobe sealed) at a pressure of 0.5 MPa is applied to the gland portion 11A,and the rotation shaft 19 is rotated at 1,900 rpm. The fastening boltsfor the packing gland 21 are adjusted so that the temperature of thegland portion 11A in the vicinity of the gland packings g is 40° C. Thetemperature is measured by the fifth thermometer 25. The leakagemeasuring unit 9 records the leakage amount after an elapse of about sixhours from a timing when the leakage amount is not changed and becomesconstant.

[Stress Relaxation Test]

With respect to stress relaxation of the gland packing g, the stressrelaxation testing apparatus C shown in FIG. 5 is used. The stressrelaxation testing apparatus C has an apparatus frame 26 including apacking mounting portion 27 into which the gland packing g is to bemounted, a packing pressing portion 28, pressing bolts 29, etc.

The apparatus has a structure where an upper portion 28 a of the packingpressing portion 28 is in spherical contact with a pressing plate 30which lays between the plurality of pressing bolts 29, and a single orplural gland packings g mounted in the annular packing mounting portion27 are pressed via an annular pressing portion 28 b.

One set of five gland packings g having an inner diameter of 100 mm, anouter diameter of 129 mm, and a height of 14.5 mm is installed in theannular packing mounting portion 27, the packings are fastened byoperating the pressing bolts 29 to set the fastening stress (initialfastening stress) p on the gland packings g to p=2N/mm², and theresidual stress after 24 hours is measured.

The stress relaxation rate σ is expressed by:

σ=p−q/p

where q indicates the fastening stress after 24 hours.

[Friction Testing Apparatus]

A friction testing apparatus D for the gland packing g will be brieflydescribed.

In the friction testing apparatus D, as shown in FIG. 6, a support frame32 and an arm 33 stand on a test frame 31. A cylinder-like rotary drum(rotation shaft) 34 which is made of a metal such as stainless steel ispivoted between the frame 32 and the arm 33, thereby configuring thefriction testing apparatus D. The rotary drum 34 can be rotationallydriven about an axis 34 a in the direction of the arrow (hollow arrow)in figure by a driving source which is not shown.

One end of the gland packing g having, for example, a square cord-likeshape is fixed to an upper portion of the support frame 32, and theother end is passed over and wound around the lower side of the rotarydrum 34, and then lifted up. A cord 35 is connected to the lifted-upother end of the gland packing g. The cord 35 is wound around a pulley36 pivoted to an upper end portion of the arm 33, and a weight 37 isattached to the other end 35 a of the cord which is vertically hung.Namely, the gland packing g is relatively rubbed against the rotary drum34 in the state where the gland packing is pressed against the surface34 a of the rotary drum 34 with a certain degree of force.

EXAMPLES

As the fibers s, acrylic fibers or modacrylic fibers are used. Thefibers have a diameter of 18 (14 to 20) μm. The LOI of the fibers wasmeasured in accordance with JIS K 7201-2 “Plastics—Determination ofburning behaviour by oxygen index—Part 2: Ambient-temperature test”.

First, the plurality of fibers are twisted to produce the yarn Y. Next,a cord-like gland packing g is produced by eight-strand square braidingin which eight yarns Y are used, or sixteen-strand circular braiding inwhich sixteen yarns Y are used, while using a braiding machine (notshown). Alternatively, the gland packing may be produced by twistedcords.

Then, the cord-like packing is formed by using a twopoint roll or afour-point roll into a square cord-like gland packing g having a squaresection in which the length of one side is 14.5 mm. The gland packing iscut into a predetermined length.

Leakage and friction tests are performed by using the thus producedgland packing g to obtain relationships among a leakage amount, atorque, and an LOI value e as shown in FIGS. 7 and 8.

In the friction test, the value of the rotary force, i.e., the torque(torque value) of the rotary drum 34 is measured while the weight 37 is1 kg, and the rotary drum 34 is rotated at 3,000 rpm. The result isshown in the table of FIG. 7 and the graph of FIG. 8.

With respect to the torque, as seen from FIGS. 7 and 8, in the case ofthe LOI value e<22, the larger the value e, the smaller the torque valueis. In the vicinity of e=22, the change amount of the torque value issmall, and, in the case of e≧22, the torque has a substantially constantvalue.

From the result, it is seen that the gland packing g is obtained inwhich, in the case of the LOI value e≧22, the friction is small, and theburden on the pump power is small. It is supposed that, as the LOI valuee becomes larger, the degree of carbonization of the fibers is moreincreased, and the friction coefficient against the rotary drum 34 isfurther reduced.

With respect to the leakage amount, as seen from FIGS. 7 and 8, in thecase of the LOI value e<27, the leakage amount has a substantiallyunchanged value, and, in the vicinity of e=27, the leakage amount isslightly increased. It is seen that, in the case of 27≦e≦30, the leakageamount shows an increasing trend, and, in the case of e≧30, the leakageamount is largely increased.

From the above, it may be said that the LOI value e is preferably,21≦e≦30, and more preferably 22≦e≦26.

With respect to a yarn formed by twisting fibers of e<21, it has beenfound that friction (friction coefficient) caused between a glandpacking which is produced by using the yarn, and a shaft (shaft of apump) is increased beyond the allowable range.

Furthermore, it has been found that a yarn formed by twisting fibers ofe>30 is poor in flexibility. When poor in flexibility, the modulus ofelasticity is high. In the case where a packing is formed by using sucha yarn, the resulting packing is hardly plastically deformed.

When poor in flexibility, the sectional shape of a square cord-likegland packing is hardly held, and rounded. Moreover, the compatibilitywith the shaft of the pump is low, and therefore the leakage amount(leakage amount per unit time) is increased.

From the above, with respect to the LOI, friction (friction coefficient)of a yarn formed by twisting fibers of the LOI value e≧21 issufficiently low, and a gland packing formed by the yarn has anexcellent slidability against a shaft.

In the case of e≧22, it is possible to provide a yarn which will beformed as a gland packing having a more excellent slidability.

In the case of e≦30, it is possible to form a yarn which can construct agland packing having a necessary flexibility. When a square cord-likegland packing is configured, namely, the sectional shape can be held,and prevented from being rounded.

Moreover, the conformability with a shaft of a pump is improved, and itis possible to attain an excellent sealing property in which lessleakage occurs.

In the case of e≦26, the gland packing has an adequate flexibility, andthe conformability with a portion which is to be sealed, such as a glandportion or rotation shaft of a pump is further improved, and thereforethe leakage amount is further reduced.

FIGS. 9 and 10 show relationships between the impregnation ratio τ andthe stress relaxation rate σ, and the flat ratio f of fibers.

In the case where the flat ratio f is f<1.1, adhesion of an impregnatingmaterial for providing the lubricating property and the sealing property(filler material) hardly occurs.

In the case where the flat ratio f is f>2, fibers are excessivelyflexible. Namely, stress is concentrated at a portion having a smallcurvature, and fibers are easily plastically deformed. When formed as agland packing, therefore, stress relaxation is large.

When a gland packing is attached to a gland of a pump and then fastenedby a packing gland, namely, stress applied to the gland packing isexcessively reduced because of plastic deformation of the gland packing.Therefore, stress in the use of the gland packing is easily relaxed, andstress necessary for sealing cannot be ensured and maintained, whereby alarge amount of leakage may be caused.

In the case where the sectional shape does not have the recess 1 (seeFIG. 2), fixation of an impregnating material for providing thelubricating property and the sealing property (filler material) hardlyoccurs.

With respect to the flat ratio f, in a gland packing in which a yarnformed by twisting fibers of f≧1.1 is used, an impregnating material iseasily held. In the case of f≧1.2, the easiness of holding of animpregnating material is further improved. In a gland packing in which ayarn formed by twisting fibers of f≦2 is used, stress relaxation can besufficiently reduced, and stress necessary for sealing can be ensuredand maintained. When the sectional shape of a fiber has the recess 1, animpregnating material is easily held by the recess, and therefore thisconfiguration is preferable.

DESCRIPTION OF REFERENCE NUMERALS

-   1 recess-   a maximum value of interval between two straight lines-   b minimum value of interval between two straight lines-   f flat ratio-   h depth of recess-   s fiber-   L1, L2 two parallel straight lines

1. A yarn wherein the yarn is formed by twisting fibers having alimiting oxygen index of 21 to
 30. 2. The yarn according to claim 1,wherein the limiting oxygen index is 22 to
 26. 3. The yarn according toclaim 1, wherein the fibers contain fibers in which a flat ratio isdefined as 1.1 to 2, the flat ratio being a value which is obtained bydividing a maximum value of an interval between two parallel straightlines in a state where a section of each of the fibers is interposedbetween the straight lines, by a minimum value.
 4. The yarn according toclaim 3, wherein the flat ratio is defined as 1.4 to 1.6.
 5. The yarnaccording to claim 1, wherein the fibers contain fibers in each of whicha sectional shape has one or more recesses.
 6. The yarn according toclaim 5, wherein a depth of the recess is 0.4 μm or more.
 7. The yarnaccording to claim 1, wherein the fibers contain modacrylic fibers. 8.The yarn according to claim 7, wherein the modacrylic fibers areacrylonitrile-vinyl acetate copolymer fibers.
 9. The yarn according toclaim 2, wherein the fibers contain fibers in which a flat ratio isdefined as 1.1 to 2, the flat ratio being a value which is obtained bydividing a maximum value of an interval between two parallel straightlines in a state where a section of each of the fibers is interposedbetween the straight by a minimum value.
 10. The yarn according to claim9, wherein the flat ratio is defined as 1.4 to 1.6.
 11. The yarnaccording to claim 2, wherein the fibers contain fibers in each of whicha sectional shape has one or more recesses.
 12. The yarn according toclaim 11, wherein a depth of the recess is 0.4 μm or more.
 13. The yarnaccording to claim 3, wherein the fibers contain fibers in each of whicha sectional shape has one or more recesses.
 14. The yarn according toclaim 13, wherein a depth of the recess is 0.4 μm or more.
 15. The yarnaccording to claim 4, wherein the fibers contain fibers in each of whicha sectional shape has one or more recesses.
 16. The yarn according toclaim 15, wherein a depth of the recess is 0.4 μm or more.
 17. The yarnaccording to claim 2, wherein the fibers contain modacrylic fibers. 18.The yarn according to claim 17, wherein the modacrylic fibers areacrylonitrile-vinyl acetate copolymer fibers.
 19. The yarn according toclaim 3, wherein the fibers contain modacrylic fibers.
 20. The yarnaccording to claim 19, wherein the modacrylic fibers areacrylonitrile-vinyl acetate copolymer fibers.